Electrical machines are known comprising a stator and a rotor with permanent magnets which is integral with a shaft. The rotor can be integral with a drive shaft and/or a driven shaft, and can belong to a rotary electrical machine in the form of an alternator or current generator as described in document EP 0 803 962, or of an electric motor as described in document EP 0 831 580. The shaft can ensure that a spiral compressor, also known as a scroll compressor, is put into motion. A system of this type comprises two interposed spirals such as vanes in order to pump and compress the coolant fluid. In general, one of the spirals is fixed, whereas the other is displaced eccentrically without rotating, such as to pump, then trap, and finally compress pockets of fluid between the spirals. A system of this type is described for example in document EP 1 865 200. In all cases, the machine comprises a housing which supports the stator. This housing is configured to support the shaft in rotation, for example by means of bearings, such as ball bearings and/or needle bearings.
The rotor comprises a body made of laminated plate, which comprises receptacles. At least one permanent magnet is positioned inside some of the receptacles. Tolerances used in the production of the rotor exist which make it possible for the magnets to be badly placed inside the receptacles of the rotor; this can be disadvantageous taking into account the action of the centrifugal force to which the magnets can be subjected. Solutions have been developed in order to remedy this aspect.
Document CN202221930 describes a rotor with permanent magnets comprising:
a set of plates forming the body of the rotor with an axis;
receptacles which are spaced regularly around the circumference of the rotor, and situated in the body of the rotor, some of which receive at least one element in the form of a permanent magnet which is retained radially and axially inside the receptacle, between an inner axial part of the receptacle and an outer axial part, the said inner axial part of the receptacle comprising two concave portions and a projecting portion which extend axially according to the axis X, the said projecting portion being radially closer to an inner axial face of the magnet than the two concave portions.
In a rotor of this type, it has been found that part of the magnetic flux created by the winding of the rotor passed via leakage paths instead of being channelled into the body of the stator. These leakages of magnetic flux take place in the vicinity of the free ends of the magnets.
It has also been found that a rotor of this type has a plurality of major disadvantages. In particular, during the fitting of the magnet in its receptacle, it is essential to provide reduced geometric tolerances of the rotor and the receptacle, in order to retain the magnet axially; more specifically, the geometric tolerances relating to the axial retention of the magnet, such as those of the hooks of the receptacle and of the projecting portion, are particularly reduced. These geometric tolerances have a negative impact on the production costs; poor adjustments could mean that it is not possible to position the magnet correctly radially, or even that it is impossible to fit the magnet inside its receptacle.